Machines have heretofore been developed for screeding paving material such as concrete and cement. Exemplary of such machines are those disclosed in U.S. Pat. Nos. 1,584,385, 2,426,702, 3,377,933 and 4,115,976. The machines today often comprise a frame that is supported by two or more drive rollers that are adapted to be driven along and atop a pair of forms that straddle a surface area to be paved which also serves as track rails for the machines. The machines have also included a screed roller at their front ends which are elevated slightly above the drive rollers and the forms. The screed rollers are driven in a reverse direction to that of the support rollers so that as the machines advance upon paving material, that has been dumped and piled between the forms, they fling and spread the material forwardly of the machine in flattening and leveling the piles of material. As the machines continue to advance, their drive rollers further smooth out the material since they are positioned slightly lower than the screed rollers.
Though the just described screeding machines have worked satisfactorily in many aspects, there has been one persistent problem attendant with their use. Specifically, these machines have been difficult to steer in an efficient manner upon the rails provided by the material confining forms. As their drive rollers must be quite wide in order to span the entire width of roadway surfaces to be paved, a slight skewing of the rollers with respect to the parallel forms causes the screeding machines, as a whole, to assume an angle of attacks with respect to the forms. As a result continued movement along such a skewed path established by an angle of attack will cause the machine to drop off of one of the forms and into the roadway bed if its forward movement is not quickly arrested. To prevent such from occurring it has typically been necessary to stop the screeding machine and then rotate it back to a proper position with its drive rollers reoriented right-angularly to the forms. Of course, where the roadway itself makes a curve, such inclemental advancements, stoppages and turnings of the machine must be done repeatedly until the roadway completes the curve and reassumes a linear direction.
This just described steering process has naturally limited the operational efficiency of these types of screeding machines. This problem may be avoided by other types of screeding machines, such as those driven with endless treads that are independently powered. This, however, is a much more costly type machine. Those driven with flanged wheels guided on the rails, such as that shown in the aforementioned U.S. Pat. No. 3,377,933, also do not have this specific problem. These, however, have other restrictions such as, for example, the need for adjustment for use in paving roads of diverse widths.
Accordingly, it is a general object of the present invention to provide a concrete screeding machine of the type that employs elongated drive rollers with enhanced steering capabilities. It is to the provision of such a machine therefore that the present invention is primarily directed.